Betsy DeVos, a billionaire philanthropist and conservative activist, has been chosen by President-elect Donald Trump to be education secretary in his incoming administration.

In a statement on Wednesday, Trump called DeVos “a brilliant and passionate education advocate”.

But she faced criticism even before it was formally announced on Wednesday afternoon. Conservatives warned that DeVos, a longtime Republican donor, previously supported the Common Core education standards that Trump railed against during the campaign.

DeVos, 58, currently heads the advocacy group American Federation for Children.

Her brother is Erik Prince, the founder of Blackwater, a private security contractor that became infamous after its operatives killed 17 Iraqis and wounded 20 more in Baghdad in 2007. Prince has since left the company, which is now called Academi.

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DeVos is a strong advocate of charter schools and allowing parents to use vouchers for private and religious schools in the name of “choice”. Teachers’ unions condemned her appointment as a blow to equality of opportunity.

Lily Eskelsen García, president of the National Education Association, said: “Her efforts over the years have done more to undermine public education than support students. She has lobbied for failed schemes, like vouchers – which take away funding and local control from our public schools – to fund private schools at taxpayers’ expense. These schemes do nothing to help our most vulnerable students while they ignore or exacerbate glaring opportunity gaps.

“She has consistently pushed a corporate agenda to privatize, de-professionalize and impose cookie-cutter solutions to public education. By nominating Betsy DeVos, the Trump administration has demonstrated just how out of touch it is with what works best for students, parents, educators and communities.”

DeVos, a former chair of the Michigan Republican party, previously supported the Common Core, the set of math and reading guidelines adopted by most states, that Trump assailed during the election campaign. She is a member of the board of the Foundation for Excellence in Education, set up by the former Florida governor Jeb Bush.

Reacting to the news of the announcement, Bush called DeVos an “outstanding pick” for the post.

“I cannot think of [a] more effective and passionate change agent to press for a new education vision, one in which students, rather than adults and bureaucracies, become the priority in our nation’s classrooms,” Bush said in a statement.

DeVos donated funds to Bush and Carly Fiorina during the Republican primary contest before endorsing Senator Marco Rubio. Like Haley, she expressed reservations about Trump. In March, she told the Washington Examiner that she considered him an “interloper” who “does not represent the Republican party”. In July she told the Associated Press: “A lot of the things he has said are very off-putting and concerning.”

The DeVos family has been active in Republican politics for decades, especially as donors to candidates and the party. Her husband, Dick, is an heir to the Amway direct sales fortune and a former president of the company.

They co-founded the Windquest Group, which invests in technology and manufacturing, and gave $22.5m to the John F Kennedy Center for the Performing Arts in Washington in 2010, then the biggest private donation in the complex’s history.